1. Field of the Invention
The present invention relates to a display device, in particular, a driver circuit for driving a display device.
2. Description of Related Art
In recent years, a flat display such as a liquid crystal display device becomes increasingly important. A typical liquid crystal display device includes a liquid crystal display panel and a driver circuit. The liquid crystal display panel displays an image and has pixel electrodes arranged in matrix. The pixel electrodes are applied with a driving voltage corresponding to an image by the driver circuit. The liquid crystal display panel has a common electrode opposite to the pixel electrode. The common electrode is applied with a common intermediate potential (common potential). The liquid crystal display panel expresses gradation in accordance with a potential difference between a pixel electrode and a common electrode to display a corresponding image.
Assuming that such a liquid crystal display device is driven with DC voltage, for example, degradation of liquid crystal components and contamination with an impurity in a liquid crystal display panel proceed, for example, burn-in of the display image or other such problems arise. To overcome the problems, an AC driving systems such as a dot-inversion driving system for varying a polarity of a driving voltage relative to the common potential from pixel to pixel has been used.
FIG. 13 is a circuit diagram showing a driver circuit for driving a liquid crystal display panel through the dot-inversion driving. As regards the dot-inversion display, a polarity of a display signal applied to a source line DL is inverted between adjacent source lines. Therefore, in the illustrated example of FIG. 13, a positive driving voltage is applied to a first source line (top line in FIG. 13) during a driving period, a negative driving voltage is applied to a second source line adjacent to the first line, and a positive driving voltage is applied to a third source line adjacent to the second source line. During a subsequent gate line driving period, the first source line is driven with a negative voltage, the second source line is driven with a positive voltage, and the third source line is driven with a negative voltage. The dot-inversion driving is realized by displaying an image with the polarity being reversed.
As shown in FIG. 13, a driver circuit 12 includes plural operational amplifiers 13 for supplying the driving voltage. In the conventional driver circuit, the output of each operational amplifier 13 is connected with the source line DL in a liquid crystal display panel 11 through a dot-inversion switch group 14.
It is assumed here that the operational amplifiers of the odd-numbered lines supply the positive driving voltage relative to the common potential, while the operational amplifiers of the even-numbered lines supply the negative driving voltage relative to the common potential. The dot-inversion switch group 14 switches between source lines to connect the selected one with the output of the operational amplifier of the even-numbered or odd-numbered line on the basis of the above gate line driving period to execute the dot-inversion driving. As a driving apparatus that executes such dot-inversion driving, an apparatus disclosed in Japanese Patent Translation Publication No. 2001-515225 is known in the art.
In the aforementioned driver circuit, a positive voltage is applied to one end of the dot-inversion switch, while a negative voltage is applied to the other end in some cases. Thus, the dot-inversion switch should be an element that never breaks due to a potential difference between the negative voltage and the positive voltage, so an element of high withstand voltage is used.
In order to improve the withstand voltage of a switch, a gate length or gate oxide film thickness needs to increase, for example. However, this results in a problem that a chip size is increased.